Method for brazing dissimilar metals and composite articles produced thereby

ABSTRACT

The invention provides a method of joining a first hard metal carbide article and a second article (preferably steel), said second article having a higher coefficient of heat expansion than said first article comprising positioning said articles adjacent each other and applying brazing filler metal to the joint between said articles and heating said brazing filler metal sufficient to braze said first and second articles together along said joint and then cooling said articles to obtain a permanent joint between them; and cooling said second article, while said brazing filler metal is being heated, sufficiently so that the amount of contraction of said second article during the cooling period subsequent to the brazing is substantially of the same magnitude as the contraction of said first article. The invention is particularly applicable to the production of elongated articles and of rimmed wheels and includes such novel composite articles.

O United States Patent 1151 3,673,677 Loqvist July 4, 1972 54 METHOD FORBRAZING DISSIMILAR 3,217,132 11 [I965 Schillinger ..29/4s7 x METALS ANDCOMPOSITE ARTICLES 3,456,333 7/1969 Meier et al ..29/487 PRODUCEDTHEREBY OTHER PUBLICATIONS [72] lnvemor: Loqvls" Fagersta Sweden A.W.S.Terms and Definitions, prepared by A.W.S. Commit- [73] Assignee:Fagersta Bruks Aktiebolag, Fagersta, lee Definitions and y 1969, PP- 46,

Sweden Primary Examiner-John F. Campbell [22] Filed 1970 AssistantExaminer-Ronald J. Shore [21] A p]. No; 8,833 Anomey-Bauer and Goodman57 ABSTRACT [30] Foreign Application Priority Data h T e inventionprovides a method of joining a first hard metal Feb. 14, Sweden carbideartic'e and a Second article (preferably Steel), i second article havinga higher coefficient of heat expansion [52] US. Cl..29/473.l,2299/1ii)71, 2294448988, than said first amide comprisingpositioning Said amides 51 l t 5 02 jacent each other and applyingbrazing filler metal to the joint E 488 between said articles andheating said brazing filler metal sufle 0 are ficient to braze saidfirst and second articles together along said joint and then coolingsaid articles to obtain a permanent 56] Rderences Cited joint betweenthem; and cooling said second article, while said brazing filler metalis being heated, sufficiently so that the UNITED STATES PATENTS amountof contraction of said second article during the coolmg perrodsubsequent to the brazing 1s substanually of the 1,75 l Lewrs et al amemagnitude as the contraction of said first article The in. 1,615,591vention is particularly applicable to the production of elon- 1 g g tgated articles and of rimmed wheels and includes such novel an even ercom osite aflicles 2,768,596 10/1956 Kalbow et al. ..29/487 X p2,986,811 6/ l96l Rudd .....29/498 X 9 Claims, 3 Drawing FiguresPATENTEDJUL 4 1972 HHH INVENTOR KAJ RAGNAR LOOVIST ATTORNEY METHOD FORBRAZING DISSIMILAR METALS AND COMPOSITE ARTICLES PRODUCED THEREBYBACKGROUND OF THE INVENTION As is will known, brazing involves joiningwith a bran'ng filler metal which at room temperature is harder and hasa higher melting point than the usual tim solder, examples of suchmetals being silver solder and copper solder. When brazing two articlestogether, they are heated to a temperature which is about the same as,or at least not less than, the melting point of the brazing fillermetal. For example, articles which are to be brazed together using aspecified quality of silver solder must be heated to about 800 C. Ifsaid articles have substantially different coefficients of heatexpansion, stresses or strains will arise in the brazed junction orjoint between them and therefore also in said articles because of thecontraction that occurs during the cooling of the articles after thebrazing operation. As an example, during brazing of a hard carbide metal(e.g. WC and/or TiC and/or TaC) to a steel article with silver solder,the latter article will contract more than the former during cooling,which has the effect that the combined body of said two articles willbend in such a way that the center of deflection will be situated on thesame side of the junction as the steel article. If this deflection orbending is strong enough, it may well happen either that the brazedjoint breaks or that the hard carbide metal article breaks or ispartially or completely detached. Therefore, brazing can be used onlyfor joints which are not too large in extension. It is an object of thepresent invention to produce composite articles by brazing two articleshaving substantially different coefficients of heat expansion.

SUMMARY OF THE INVENTION The present invention comprises a processwhereby an article having a higher coefficient of heat expansion iscooled under controlled conditions during the brazing operation, so

that its subsequent contraction, when the combined body has cooled atthe end of the brazing operation, is of substantially the same magnitudefor both of the two articles being joined. This results in eliminatingthe strains in the brazed joint. The method of the present inventionthus provides a brazed joint which is practically neutral with regard toso called macrostrain, whereas the so called microstrain (strains in thebrazed junction) depends on the thickness of the brazed junction itselfand the extension of the heated zone during the brazing process.

BRIEF DESCRIPTION OF THE DRAWING FIG. isa perspective view of acomposite body mounted with cooling plates in operative position forcooling during a brazing operation;

DESCRIPTION OF THE PREFERRED EMBODIMENTS In its broadest aspects thepresent invention provides a method of joining a first article and asecond article, said second article having a higher coefficient of heatexpansion than said first article comprising positioning said articlesadjacent each other and applying brazing filler metal to the jointbetween said articles and heau'ng said brazing filler metal sufficientto braze said first and second articles together along said joint andthen cooling said articles to obtain a permanent joint between them; andcooling said second article, while said brazing filler metal is beingheated sufliciently so that the amount of contraction of said secondarticle during the cooling period subsequent to the brazing issubstantially of the same magnitude as the contraction of said firstarticle.

The method of the present invention is particularly useful tomanufacture elongated articles and/or round or circular or flat articleshaving a rim or circular segment attached to a flat side prepared byjoining an elongated hard metal carbide article with a second article,said second article having a higher coefficient of heat expansion thansaid hard metal carbide article comprising positioning said articlesadjacent each other and applying brazing filler metal to the jointbetween said articles and heating said brazing filler metal sufiicientto braze said articles and then cooling said articles to obtain apermanent joint between them; and cooling said second article, whilesaid brazing filler metal is being heated, sufficiently so that theamount of contraction of said second article during the cooling periodsubsequent to the brazing is substantially of the same magnitude as thecontraction of said elongated hard metal carbide article.

The foregoing methods permit the manufacture of novel articles includinga composite wheel having a hardened steel body rimmed with a hard metalcarbide peripheral surface rim, said hard metal carbide peripheralsurface being physically in contact with said steel body along thecentral portion of the periphery of said steel body; said hard metalcarbide rim being brazed to said hard metal steel body by means of twobrazed joints, one of said brazed joints being between said hard metalcarbide rim and said steel body along one side of said periphery and theother of said brazed joints being along the other side of saidperiphery, said joints being separated by the central portion of saidhard metal carbide rim physically in contact with said steel body.

In the specification herein, the term wheel is used in its broadestsense and is generic to such devices as pulleys, drums, gears, bosses,etc.

The hard metal carbide articles are illustrated by such tool materialsand/or wear resistant materials as tungsten carbide and/or titaniumcarbide and/or tantalum carbide. These materials may be sintered orcemented carbides.

The amount of cooling of the article having the higher coefficient ofheat expansion carried out during the brazing operation is dependentupon the particular materials of which the articles are constructed, thesize and shape of the article and the joint, the type of brazing fillermetal and the process conditions utilized during brazing, i.e., amountand rate of heat application, etc. In each case the amount of coolingnecessary is readily determined for each operation. The result of thecooling is that the article being cooled is not so heated during thebrazing operation that it expands greatly with a consequent greatercontraction which causes the macrostrains and rnicrostrains referred tohereinbefore. The cooling is utilized to allow only sufficient expansionthat the consequent contraction is of the same magnitude as thecontraction of the article having the lower coeflicient of heatexpansion. The term same general magnitude is used to encompass thosesmall difierences in contraction which do not result in an unsound jointfor the service conditions contemplated.

The invention is further illustrated by reference to the drawings withinitial reference to FIGS. 1 and 2. A rod 1 of hard carbide metal, e.g.,WC, is to be brazed to a steel rail 2. Said steel rail 2, which has thehigher coefficient of heat expansion, is cooled by two clamping bars 3of copper. Said cooling is controlled in such a manner that parts ofsaid steel rail 2 (the cooled part) is maintained at a specifiedtemperature with respect to the temperature of the rod 1 of hard carbidemetal. Said clamping bars 3 may be cooled by a cooling liquid, forexample water, which flows through the clamping bars and which ismaintained at a specified temperature. The clamping bars 3 may be cooledby passing the cooling water through longitudinal openings 10 runningentirely through each of the clamping bars 3.

By carrying out the brazing operation and therefore also the heatingsuccessively from one end of the junction 11 to the other end, andbecause the steel rail 2 is cooled at all times during the brazingoperation, only local differences in expansion between the rod 1 andsteel rail 2 will occur. It is important that the temperature of thesteel rail 2 should not be lowered too greatly, i.e., excessive coolingapplied to the steel rail 2. This could result in such a severe controlof the heat expansion of the steel rail 2 that it is actually less thanthe expansion of. the rod 1 and in that instance the rod 1 could act asif it were the article having the higher coeflicient of heat expansionand contract excessively relative to the contraction of the steel rail2.

In accordance with the foregoing, a tungsten carbide rod 1 may be brazedto a hardened steel rail 2 utilizing a silver-base brazing filler metalby the application of heat sufficient to raise the temperature of thebraze filler metal and the temperature of the. surfaces of rod 1 andsteel rail 2 meeting at junction 11 to about 800C. 7

FIG. 3 shows, in section, how a ring4 of hard carbide metal can bebrazed to a hardened steel roller body or steel boss 5 of a so calledKocksblock for wire rolling. A brazed joint 8 is to be madealong theedges of the joint between the ring 4 and the boss 5, whereas at thecentral portion 9 of the joint the ring shall have direct contact withthe boss 5, so that the rolling pressure can be transmitted directlyfrom the ring 4 to the boss 5. Acorresponding brazed joint 12 is to bemade along the other side of the central portion 9. During the brazingoperation the boss 5 is cooled through a circular cooling body 6 ofcopper, through which cooling water is passed through channels 7.Previous to the present invention it has been considered as impossible.to achieve brazed joints of this kind, that is to say brazed hardenedsteel, because the hardening was lost by the heating during the brazingoperation.

Utilization of the invention is not confined to those examples which aregiven about but embraces all operations and composite articles whichfall within the scope of the claims.

What is claimed is:

1. The method of joining a first hard metal carbide article and a secondmetal article, said second article having a higher coelficient of heatexpansion than said first article comprising positioning said articlesadjacent each other and applying articles to obtain a permanent jointbetween them; and cooling said second article, .while said brazingfiller metal is being heated, sufficiently so that the amount ofcontraction of said second article during the cooling period subsequentto the brazing is substantially of the same magnitude as the contractionof said first article.

2. The method of claim 1 wherein said second article is cooled bycontacting said article with a hollow metal plate and passing coolingwater through said hollow metal plate to cool said second article.

3. The method of claim 2 wherein said second article is a steel article,and said brazing filler metal is a silver-base brazing filler metal.

4. The method of claim 2 wherein said brazing filler metal is acopper-base brazing filler metal.

5. The method of joining an elongated hard metal carbide article .with asecond article, said second article having a higher coefficient of heatexpansion than said hard metal carbide article comprising positioningsaid articles adjacent each other and applying brazing filler metal tothe joint between said articles and heating said brazing filler metalsufficient to braze said articles and then cooling said articles toobtain a permanent joint between them; and cooling said second article,while said brazing filler metal is beirig heated, sufficiently so thatthe amount of contraction of said second article during the coolingperiod subsequent to the brazing is substantially of the same magnitudeas the contraction of said elongated hard metal carbide article.

6. The method of claim 5 wherein said second article is a ferrous metalarticle.

7. The method of claim 6 wherein said second article is a hardened steelarticle.

8. The method of claim 7 wherein said second article is a steel rail andsaid hard metal carbide article is a continuous strip surfacing at leasta portion of one surface of said steel rail.

9. The method of claim 7 wherein said second article is a wheel andwherein said elongated hard metal carbide article is a ring which ispositioned and brazed around the periphery of said wheel.

2. The method of claim 1 wherein said second article is cooled by contacting said article with a hollow metal plate and passing cooling water through said hollow metal plate to cool said second article.
 3. The method of claim 2 wherein said second article is a steel article, and said brazing filler metal is a silver-base brazing filler metal.
 4. The method of claim 2 wherein said brazing filler metal is a copper-base brazing filler metal.
 5. The method of joining an elongated hard metal carbide article with a second article, said second article having a higher coefficient of heat expansion than said hard metal carbide article comprising positioning said articles adjacent each other and applying brazing filler metal to the joint between said articles and heating said brazing filler metal sufficient to braze said articles and then cooling said articles to obtain a permanent joint between them; and cooling said second article, while said brazing filler metal is being heated, sufficiently so that the amount of contraction of said second article during the cooling period subsequent to the brazing is substantially of the same magnitude as the contraction of said elongated hard metal carbide article.
 6. The method of claim 5 wherein said second article is a ferrous metal article.
 7. The method of claim 6 wherein said second article is a hardened steel article.
 8. The method of claim 7 wherein said second article is a steel rail and said hard metal carbide article is a continuous strip surfacing at least a portion of one surface of said steel rail.
 9. The method of claim 7 wherein said second article is a wheel and wherein said elongated hard metal carbide article is a ring which is positioned and brazed around the periphery of said wheel. 